Epoxy/graphite composite electrode modified with recycled silver nanoparticles: An eco-friendly strategy to improve lead detection

In this work, silver nanoparticles (AgNPs) obtained from photographic waste were synthesized and electrodeposited via cyclic voltammetry using epoxy-graphite composite as an electrochemical substrate. Both electrodes, unmodified (Epoxy/C) and modified (Epoxy/C/AgNPs), were characterized electrochemically by electrochemical impedance spectroscopy (EIS), charge transfer constant (K⁰), and electroactive area. The modified electrode provided lower charge transfer resistance (275 Ω), more kinetically favored electron transfer (K⁰ = 1.15 × 10^-3 cm s^-1), and a 1.7-fold increase in the active area compared to the unmodified electrode. Additional characterizations by scanning electron microscopy (SEM) and Raman spectroscopy confirmed the presence of AgNPs structures on the carbonaceous surface. As a proof of concept, Pb²⁺ was used as a model analyte, and a square wave anodic stripping voltammetry (SWASV) method was developed to evaluate the analytical performance of both electrodes. A wider linear range (4.0 to 40.0 μg L^-1), the appropriate limit of detection (1.2 μg L^-1), and a 6-fold increase in sensitivity were found using the modified electrode, suggesting that the AgNPs significantly contributed to the performance of the electrode. The proposed method was applied to three real water samples, where the Pb²⁺ levels varied from 11.3 to 19.5 μg L^-1. The proposed protocol (reuse of silver waste) has proven to be a powerful tool for improving the detection of Pb²⁺, which can be helpful for other electrochemical sensing applications in locations with minimal infrastructure. (author)